1. Technical Field of the Invention
The present invention generally relates to computer systems. More particularly, and not by way of any limitation, the present invention is directed to a system and method for power management in a computer system having multiple power grids.
2. Description of Related Art
The reliability and quality of a computer system depends on properly protecting the hardware components of the computer system against power disturbances. Power disturbances can be divided into several categories. Noise or static is a minor disturbance characterized by a small change in voltage. A transient, sometimes called a spike or surge, is a disturbance characterized by a very short, but extreme burst of voltage. Brownouts and blackouts are severe disturbances characterized by the temporary drop and complete loss of electric power, respectively.
Of these disturbances, blackouts pose a serious threat to today's computer systems which heavily rely on volatile memory components that are particularly susceptible to power interruptions. Prior to shutting down a computer system, it is important to ensure that no portion or segment of the system is in a condition of instability. In a blackout, a complete power interruption causes the instant shutdown of a computer system thereby disrupting and destabilizing the transfer and storage of data. The data may be lost or corrupted or placed in an unpredictable form.
Therefore, it is essential that a computer system avoid power interruptions and maintain extended availability or “uptime.” To provide uptime, many computer systems are equipped with multiple power grids that are powered by one or more AC power lines. To provide redundancy in the system, each AC power line may be operating on a separate breaker. Moreover, to provide further redundancy, the AC power lines may be connected to multiple municipal power grids. When a particular AC power line loses power, the power grid may continue to maintain power to the system from an alternative AC power line.
Although these computer systems are provided with redundant AC power sources to guard against power interruption, such systems are not without limitations. In many instances, connecting AC power lines to multiple municipal power grids is prohibitively expensive. Moreover, even if a computer system is connected to multiple municipal power grids, an area-wide power outage over several municipalities or similar single point fault can bring down the computer system. To overcome these types of single point faults, computer systems employ uninterrupted power supplies (UPSs) that are typically equipped with a battery and a loss-of-power sensor. When the UPS detects a power failure, it switches over to the battery so that the computer system may remain operational. If power service does not resume, the UPS sends a power loss notification to the operating system (OS) so that the OS may begin an orderly and graceful shutdown.
It has been found, however, that UPS-based arrangements are not without limitations either. Regardless of the availability of alternative sources of power, when an UPS detects a power failure and power does not resume, the UPS sends a power loss notification to the OS thereby effectuating a shutdown. More specifically, an UPS detecting a sustained power failure will send a power loss notification to the OS even when an AC power line or second UPS is available as an alternative power source. Therefore, the existing power management systems employing one or more UPSs needlessly begin shutdowns in the event of a power failure.